Massive neutrino detector narrows hunt for hidden fourth neutrino
IceCube Observatory has set new constraints on theoretical "sterile neutrinos" that could explain dark matter and other cosmic mysteries. The analysis rules out certain mass and mixing scenarios, refining what physicists need to look for—and potentially informing long-term energy and fundamental physics research priorities.
Originaltitel: Exploration of mass splitting and muon/tau mixing parameters for an eV-scale sterile neutrino with IceCube
<p>We present the first three-parameter fit to a 3+1 sterile neutrino model using 7.634 years of data from the IceCube Neutrino Observatory on nu(mu) + (nu) over bar (mu) charged-current interactions in the energy range 500-9976 GeV. Our analysis is sensitive to the mass-squared splitting between the heaviest and lightest mass state (Delta m(41)(2)), the mixing matrix element connecting muon flavor to the fourth mass state (vertical bar U-mu 4 vertical bar(2)), and the element connecting tau flavor to the fourth mass state (vertical bar U-tau 4 vertical bar(2)). Predicted propagation effects in matter enhance the signature through a resonance as atmospheric neutrinos from the Northern Hemisphere traverse the Earth to the IceCube detector at the South Pole. The remaining sterile neutrino matrix elements are left fixed, with vertical bar U-e4 vertical bar(2) = 0 and delta(14) = 0, as they have a negligible effect, and delta(24) = pi is set to give the most conservative limits. The result is consistent with the no-sterile neutrino hypothesis with a probability of 4.3%. Profiling the likelihood of each parameter yields the 90% confidence levels: 2.4 eV(2) < Delta m(41)(2) < 9.6 eV(2), 0.0081 < vertical bar U-mu 4 vertical bar(2) < 0.10, and vertical bar U-tau 4 vertical bar(2) < 0.035, which narrows the allowed parameter-space for vertical bar U-tau 4 vertical bar(2). However, the primary result of this analysis is the first map of the 3+1 parameter space exploring the interdependence of Delta m(41)(2), vertical bar U-mu 4 vertical bar(2), and |U-tau 4 vertical bar(2).</p>